It is essential for a dental prosthesis (e.g. a crown, a bridge, an implant, etc.,) to be as close as possible in color to the adjacent teeth.
At present, the color of a dental prosthesis is determined at sight, in general by a dentist comparing color samples with the teeth of the patient. This procedure gives results that necessarily depend on the dentist's capacity to distinguish between colors which are very similar, which is sufficient reason for results that are not always very satisfactory.
It may also happen that a prosthesis color selected in this way is very close to the color of the adjacent teeth so long as the teeth are illuminated by a light source giving a generally uniform spectrum, but that the prosthesis color appears quite different when the teeth are illuminated by a light source such as a fluorescent tube which radiates a spectrum concentrated in a few lines (a phenomenon sometimes known as metamerism).
Colorimeters exist which measure the color of an object by using filters to determine the tristimulus values X, Y, and Z of the object's color, thereby enabling said color to be reproduced by mixing three primary colors. However, a knowledge of the tristimulus values applicable for any given illumination is not sufficient for specifying the values under different illumination. Thus, in order to obtain good results using colorimeters it is necessary to take a large number of color measurments under different lighting conditions, which is a considerable problem.
The invention seeks to mitigate this problem.
An aim of the invention is to provide a method and apparatus for determining the apparent colors of an object corresponding to various different types of illumination, on the basic of a single measurement performed under unspecialized illumination.
Another aim of the invention is to provide a method and apparatus of the above-mentioned type suitable for performing such measurements on objects which are difficult of access, such as a person's teeth.